Convert Item class hierarchy to disciminate union

[kharus]

No description provided.

[Copilot]

Pull Request Overview

This PR converts the Item class hierarchy into a discriminated union by replacing classes with interfaces and helper functions while updating the nnf transformation logic and corresponding tests.

• Refactors Item.ts to use interfaces and pure functions instead of class inheritance.
• Updates tests in tests directories to leverage the new discriminated union model and helper functions.
• Adjusts the Relevance.ts file to use the new Item structure.

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/model/Item.ts	Conversion from classes to interfaces; addition of helper functions and a top‑level nnf function.
src/model/tests/Item.test.ts	Updates tests to use the new helper functions and nnf function.
src/model/Relevance.ts	Refactors instance checks to switch on item.type; modifies getChildren behavior.
src/model/tests/Relevance.test.ts	Updates test imports and instantiation to use new helper functions.
src/model/tests/ViewHide.test.ts	Adapts tests to align with the new Item model via helper functions.

Comments suppressed due to low confidence (1)

src/model/Relevance.ts:50

• For a 'Not' item, the original behavior returned its child in an array. Now, recursively calling getChildren may omit the child when item.child is a leaf. Consider returning [item.child] for 'Not' to preserve the prior behavior.

case 'Not': return getChildren(item.child);